1. Field of the Invention
The present invention relates to an ultrasonic transmitting and receiving apparatus and an ultrasonic transmitting and receiving method to be used for observing internal organs in a living body and the like by transmitting and receiving ultrasonic waves.
2. Description of a Related Art
Conventionally, to obtain a three-dimensional image by transmitting and receiving ultrasonic waves, a one-dimensional sensor array with positional sensors has been used, and a two-dimensional image of a cross section in the depth direction is obtained by electrically steering the transmitting ultrasonic waves, and further, plural two-dimensional images obtained by mechanically shifting the one-dimensional sensor array are synthesized into a three-dimensional image. However, according to this technique, since there resides a time lag in the mechanical shift of the one-dimensional sensor array, plural two-dimensional images of different points of time are synthesized resulting in a blurred synthesized image. Accordingly, the technique is not suitable for imaging of objects having motion like a living body.
In order to eliminate the problem as described above, it is advantageous to obtain three-dimensional images by using a two-dimensional sensor array. However, since the number of ultrasonic detection elements included in the two-dimensional sensor array is extremely large compared to the one-dimensional sensor array, another problem arises. For example, when a two-dimensional sensor array of approximately 80×80 elements is used, it is ideal to receive ultrasonic waves by using all elements. However, when the number of the elements is large, such problem arises, that is, the wiring in manufacturing of the two-dimensional sensor array becomes complicated. Further, as to a number of channels of electrical circuits for processing detection signals obtained by detecting ultrasonic waves with the ultrasonic detection elements, since the same number of channels as a number of the ultrasonic detection elements are required, such another problem arises, that is, the electrical circuits become complicated.
Under such circumstances as described above, in order to reduce the number of channels of the electrical circuits for processing the detection signals, a “sparse array” is used, in which only partial ultrasonic detection elements in the two-dimensionally disposed plural ultrasonic detection elements are used.
For example, U.S. Pat. No. 6,241,675 B1 discloses, in an ultrasonic measurement system for measuring velocity of tissue, a sparse array in which transducers are selectively connected. Also, an arrangement of a sparse array adapted so as to obtain a satisfactory acoustic field by reducing side lobes is disclosed by Richard E. Davidsen et al. “TWO-DIMENSIONAL RANDOM ARRAYS FOR REAL TIME VOLUMETRIC IMAGING”, ULTRASONIC IMAGING 16 (1994), (Academic Press Inc.), pp. 143–163.
However, when performing sector scan of a wide range of area, sometimes side lobes are generated in a specific direction. According to the above conventional art, the wiring connection, which has been once set up, is fixed and the arrangement thereof is hardly changed, and therefore, even when side lobes are generated in a specific direction, the side lobes can not be reduced. The side lobes lead to generation of an artifact (virtual image) or the like on the images obtained by ultrasonic imaging, which accelerates deterioration of the image and reduces the quality of image.